Generally, if a state of charging of a battery is lowered below a predetermined value, a portable electronic device comes to a power-saving mode in order to protect data under working using the portable electronic device or prevent any abnormal operation caused by the battery in a state of low charging, thereby allowing the portable electronic device to operate stably.
However, the charging capacity of the battery is frequently measured erroneously due to the number of charging the battery, an abrupt temperature change of surroundings, instability of a battery pack, or the like.
In more detail, a battery pack (or, a secondary battery) such as a lithium-ion battery becomes unstable when it is turned off just after charging/discharging and then it is turned on again, so an open voltage of the battery pack may be not corresponding to a real charging capacity.
In case the open voltage of the battery pack is not corresponding to a real charging capacity as mentioned above, a charging capacity calculated based on the open voltage of the battery pack becomes inaccurate.
This battery pack becomes stable after a predetermined power-off duration time. Thus, it has been strongly pursued to develop a technique capable of improving calculation accuracy of a state of charging by calculating a power-off duration time and then calculating a state of charging of a battery in different ways depending on the calculated power-off duration time.